To save fuel and to reduce the carbon dioxide emissions of an internal combustion engine, various measures have been proposed over the last years to provide a coolant conveyance in the coolant circuit of an internal combustion engine that is adapted to actual needs. In this context, one has to differentiate between electrically driven pumps where the coolant flow is changed by adjusting the rotational speed of the electric motor, and mechanically driven pumps, operated via a belt or chain drive, where the coolant flow is varied either via hysteresis clutches or changes in the inflow or outflow geometries in the area of the pump blade wheel. Compared to electric pumps or pumps with a hysteresis clutch, a control through a change in the inflow or outflow geometry is often clearly more economically realized.
Variable coolant pumps have thus been recently developed where the outlet cross section can be closed by means of a substantially pot-shaped valve element that is arranged for axial displacement in the pump housing. Mostly, the pot-shaped valve element is displaced using a solenoid acting on the pot-shaped valve element against a spring force so that, when the magnet is energized, the outlet cross section of the pump blade wheel is closed. Such coolant pumps are described, for example, in DE 10 2005 004 315 A1 or DE 10 2004 054 637 A1.
Drawbacks of these prior art embodiments are the rather high control effort of the solenoid and the rather large space required for accommodating a solenoid of enough strength to displace and support the pot-shaped valve element.
Coolant pumps are described in WO 2004/059142 A1 and WO 2007/025375 A2, wherein guide blades are arranged at the inlet in front of the blade wheel of the pump in order to control the incident flow to the blade wheel and thus the volume of coolant conveyed. To this end, the guide blades are swiveled approximately around their central axes via a turnable ring. These prior art embodiments are disadvantageous in that either the incident flow to the pump head has to be radial because the pump is driven on the suction side, or additional axial installation space is required for the accommodation of the guide blades. When the installation space is limited, the actuator has to apply a rather high torque in order to adjust the guide blades.
A centrifugal pump with adjustable guide vanes is described in DE 736 266, which are arranged in the vicinity of the pump's diffuser behind the blade wheel. These guide blades are also turned approximately about their central axes in order to avoid the occurrence of wobbling. Again, great actuating forces and high torques have to be applied by the actuator.